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Powered hub and micro USB both powering the pi is it safe?

Posted: Wed Jun 26, 2013 1:57 pm
by VishmanX
So I recently got a RPi model b which I'd bought a relative for Christmas in 2012. However the said family member never used it so they told me to learn to program with it. Now I'm a total noob with this stuff as I am only 14. I bought a inland 7 port hub with power, but when I plug it in it powers my RPi. Now because the hub was VERY cheap only $8 at Microcenter, I don't trust it so I want to also have micro USB power hooked up. My question is, will this be safe? I bought the pi December 2012 so I believe it is V2 but I still have no clue about any of it. Either way thanks for any help.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 2:32 pm
by DaveDriesen
The hub should not backpower the pi (it is not safe as this bypasses the pi's polyfuse which can cause serious damage).

Search the forums for similar topics and extensive explanations by the authoritative guru's.

Dave Driesen
Linux dev and oldskool elite

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 2:46 pm
by VishmanX
I thought v2 didn't have fuses, is there a way to stop this the backfeeding, and another question how much power for raspbian's GUI?

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 3:06 pm
by redhawk
Open the hub and cut the red wire, this should stop the Pi from being powered via backfeeding.

Richard S.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 3:36 pm
by rpdom
VishmanX wrote:I thought v2 didn't have fuses, is there a way to stop this the backfeeding, and another question how much power for raspbian's GUI?
The Rev 2 (and late Rev 1s) didn't have the polyfuses F1 and F2 on the USB power outputs, but all Pis have F3 on the microUSB power input. Feeding power in anywhere else will bypass that fuse.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 3:41 pm
by pluggy
I wouldn't worry about it myself.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 3:45 pm
by VishmanX
So how do I stop the back feeding though?

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 4:26 pm
by rpdom
VishmanX wrote:So how do I stop the back feeding though?
Either cut open the cable and chop the (usually) red wire and tape it back safely, or open the hub and cut the circuit where the power comes in from the USB from the Pi. The first option is easier and safer and you can always replace the cable if you get it wrong.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 10:13 pm
by VishmanX
Yet another question on this subject, will cutting the red cable in the USB cable, cause any problems with the hub or cable? I just don't want
To screw stuff up

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Wed Jun 26, 2013 11:03 pm
by redhawk
The USB port only requires 3 connections for communications the other connector merely provides power to the attached device.
Since your hub already has an external power source it's perfectly safe to cut the red wire to disconnect the power from the Pi.
Some hubs are designed to be powered by the host or via an external power supply unfortunately the poorly designed ones don't prevent backfeeding like they should.

Richard S.

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Thu Jun 27, 2013 2:11 am
by rpdom
I have heard of only one type of hub that cutting the red cable didn't work on.

That was an expensive, powered, hub that wouldn't turn on unless it saw power on its USB input as well as the PSU. Normally a powered hub that senses the host power like this will not back-power, so doesn't need the wire cutting.

The cheap ones don't sense the input power, they just connect all the 5V power lines together internally and don't control them at all.

So, go ahead. it is 99.999% likely to work, and if it doesn't you can replace the cable cheaply. :)

Re: Powered hub and micro USB both powering the pi is it saf

Posted: Sun Jun 30, 2013 3:29 am
by toadslinger
Micro center is not exclusive to Houston, but, are you by chance in Houston? If so I know of 2 local people that have successfully booted the Pi, and could offer some support.